The police and government's five-year attempt to keep secret evidence relating to a man shot dead by police is wrong, an inquiry today heard.

A police officer shot Azelle Rodney six times from point blank range in a street in Edgware, north London, in April 2005.

Since then police and the government have said the information that led officers to follow Rodney, and for one to shoot him, had to be kept secret. It is believed to have come from electronic intercepts.

The dead man's family fought plans for an inquest into the death to be held in which secret evidence would be withheld from them and their lawyers. Consequently, there has been no inquest and the family said their right under article two of the European Convention on Human Rights to an independent inquiry into the state killing of their loved one could not be met.

Today an inquiry into the death began in London, chaired by a former high court judge, Sir Christopher Holland.

Counsel to the inquiry, Ashley Underwood QC, rejected the government's central premise that the crucial evidence covering why police opened fire would have to be kept secret from the family of the deceased, their legal team and the public.

"It will be my submission throughout that it will be entirely possible to hear this matter sufficiently in public with sufficient engagement of the family so as to discharge the state's article two obligations by way of this inquiry," he said.

The Guardian understands the evidence relates to intercepted communications, such as phone intercepts.

The government and police believed the laws covering this, contained in the Regulation of Investigatory Powers act (Ripa), meant it could not be disclosed to an inquest or inquiry.

Holland will now decide whether to rule that the evidence can be revealed, and if he does so, it is expected the government will consider a legal challenge.

The Rodney case was one reason the last government tried to change the law to allow "secret" inquests to be held. The attempt eventually failed.

The police belief that Ripa meant they could not share material from intercepts with unauthorised persons also meant that officers were told by their bosses to give incomplete statements to an investigation into the death conducted by the Independent Police Complaints Commission.

The officers are now expected to give complete statements, over five years after the shooting, before the inquiry resumes next year.

Rodney, from Hounslow, west London, was in a silver Golf car outside the Railway Tavern in Burnt Oak in April 2005 when he was confronted and shot by armed police six times in the face, head, neck and chest. Weapons were later found in the car.

The car had been under police surveillance before officers stopped the vehicle at about 8pm on 30 April 2005.

Two men in the front, both aged in their 20s, escaped uninjured and were later jailed for firearms offences.

Rodney's mother, Susan Alexander, has fought a five-year battle for answers as to why one officer, known only by the codename E7, believed it was necessary to open fire.

Her barrister Tim Owen QC said: "Susan Alexander is not a fool and she is sick and tired of being patronised, of being marginalised, of being treated as an irrelevant nuisance by what is to her a bewildering legal obstacle course with no apparent end.

"She simply wants to know in unsanitised, unedited form why police officer E7 believed it was necessary to shoot her son six times at point blank range in a car on a busy London street."

The Crown Prosecution Service later decided that no officer should face criminal charges.

The public inquiry was announced in March after an inquest stalled in 2007 over the Metropolitan police's refusal to disclose secret evidence to the coroner.

Today's ruling by the inquiry chair saying evidence the government wants kept secret can in fact be made public, and other legal arguments, means it is not expected to start hearing evidence from witnesses until March next year.